Varying angles along a single cutting edge are known from numerous publications, e.g. from U.S. Pat. No. 6,991,409, and the article “Variations on a theme” (Cutting tool engineering magazine, October 2004, Volume 56, Number 10).
In the above-mentioned article, it is noted there are different usages of the term “variable”. In the present application, such usage is directed to a single peripheral edge which has an angle that has at least one different value at different axial locations therealong (i.e. the angle is not compared to angles of other cutting edges circumferentially spaced about the end mill, separated by flutes, but rather along the same edge). It will be understood that such end mill can also include additional cutting edges on other teeth of the end mill which have variable angles along their respective axial lengths, and which also may be different to other cutting edge values at the same axial location.
In the above publications, variable angles are utilized to reduce chatter, which in turn can increase tool life. While all features of an end mill are typically connected to improving tool life, the subject matter of the present application uses variable angles in a different way to improve tool life.
In particular, the present application is believed beneficial for end mills designed to mill using peripherally extending cutting edges (i.e. edges extending along a basic axial direction of an end mill rather than edges located at a cutting end face of an end mill). For example, shouldering applications use peripherally extending edges to mill around an external periphery of a workpiece, typically, but not limited to, a depth equal to the diameter of the end mill (“1D”) or often a depth twice the diameter (“2D”). Similarly, slotting applications can use the peripheral edges of the mill to enter a workpiece to create a slot or like-shapes at similar depths. It should be understood that the terminology of “end mill configured for shouldering and/or slotting applications” is not intended to exclude end mills which are also configured for facing operations (i.e. milling using axial edges at the cutting end face) but is intended to exclude end mills configured for facing operations only and not configured for shouldering and/or slotting operations (i.e. face mills).
For succinctness, all of the angles discussed herein are to be understood as relating to a peripherally extending cutting edge or tooth and not an axial cutting edge or tooth located at a cutting end face or even a corner cutting edge extending between an axial tooth and a peripheral tooth. Thus, the abbreviated name “cutting edge” can be used below instead of “peripheral cutting edge”. Accordingly, it will be understood that the term rake angle herein could more specifically be called a radial rake angle. This should not be understood to mean a given tooth does not also comprise an axial cutting edge or axial rake angle.
Generally speaking, in the specification and the claims, unless an angle is stated to be the “same” along a given sub-edge, said angle can be variable. For example, when stated that a cutting edge has “a helix angle” there may be different helix angles along the sub-edge, i.e. a range of angles.